Records of Indosinian Orogenesis in Lhasa Terrane, Tibet     

Li Huaqi  Xu Zhiqin  Yang Jingsui  Cai Zhihui  Chen Songyong  Tang Zemin 《中国地质大学学报(英文版)》2009,20(2)

Based on the deformation characteristics of the ductile shear zones in Sumdo (松多) Group, the quartz fabric by EBSD (electron backscatter diffraction), the data of muscovite 40Ar-39Ar geochronology (220-230 Ma) from ductile shear zones and the zircon SHRIMP U-Pb chronology (190 Ma) of granites in Snmdo region, Lhasa (拉萨) terrane is thought to have experienced an important Indosinian orogenic event at 220-230 Ma, which caused the closure of the paleo-Tethys Ocean along the tectonic zone of eclogite and the collision between northern part and southern part of the Lhasa terrane. The zircon SHRIMP U-Pb chronology of 190 Ma for biotite adamellite, with the distributing characteristics of the granite massif intruding in Sumdo Group, indicates that the biotite adamellitc should be the late orogenic or post-orogenic granite resulting from the lndosinian orogenesis. The discovery of Indosinian orogenic belt in Lhasa terrane expansed the southern boundary of lndosinian orogenic belt in Qinghai (青海)-Tibet plateau to Lhasa terrane from Qiangtang (羌塘) terrane, which changed the understanding about the distribution of Indosinian orogenic belt in Qinghai-Tibet plateau and extended the "T" type lndosinian orogenic belt in China. The study is very important for the formation and distribution of paleo-Tethys Ocean in Tibet. The ancient terrane framework and evolution of Qinghai-Tibet plateau need further research.  相似文献   

Statistical analysis of soil variability in a humid forest landscape of Central Cameroon     

《International Journal of Applied Earth Observation and Geoinformation》2004,5(1):69-79

The quantitative evaluation of key factors of soil variability together with the spatial pattern of underlying variables are important steps in understanding the functioning of soilscapes. Fifteen physical and chemical variables describing 24 pedons were used to elucidate processes of soil differentiation in a humid forest environment in Southern Cameroon. Landscape positions delineated on the basis of remote-sensed imageries included flat convex summits (FCS), linear valley slopes (LVS), colluvial inland valleys (CIV), and alluvial floodplain. Ordination by principal component analysis (PCA) resulted in a three-factor model, which efficiently summarized the dataset explaining 81.4% of total soil variance (TSV). The pedogenetic factor of ferralitization emerged as the main factor accounting for 43.7% of TSV. Identified underlying processes included basic cation leaching, solum acidification, and in situ clay build up. Cation exchange properties as influenced by organic constituents and soil available P were the second and third most important factors associated with 26.7 and 11.4% of TSV respectively. Organic constituents and related biological processes had strong control on nutrient availability and cation-exchange properties, while soil available phosphorus (AP) showed a strong dependence on potential acidity and organic matter mineralization status. The analysis of variance highlighted significant differences for most soil properties across landscape position and soil depth except for organic carbon (OC), total nitrogen (TN), and total phosphorus. All the soils, however, have low pH, low basic cation saturation, and correlatively high exchangeable Al irrespective of their position in the landscape.  相似文献   

Paleogene magmatism and gold metallogeny of the Jinping terrane in the Ailaoshan ore belt,Sanjiang Tethyan Orogen (SW China): Geology,deposit type and tectonic setting     

《Ore Geology Reviews》2017

The Jinping terrane is situated in the southern segment of the Ailaoshan ore belt, Sanjiang Tethyan Orogen (SW China). The Paleogene intrusions in Jinping consist of syenite porphyry, fine-grained syenite and biotite granite stocks/dikes, and contain relatively low TiO₂ (0.21–0.38 wt%), P₂O₅ (0.01–0.35 wt%), and high Na₂O (2.00–4.62 wt%) and K₂O (4.48–7.06 wt%), belonging to high-K alkaline series. Paleogene gold mineralization in Jinping comprises four genetic types, i.e., orogenic, alkali-rich intrusion-related, porphyry and supergene laterite. The NW–NNW-trending faults and their subsidiaries are the major ore-controlling structures. The orogenic Au mineralization, dominated by polymetallic sulfide-quartz veins, occurs in the diorite and minor in Silurian-Devonian sedimentary rocks. It contains a CO₂-rich mesothermal fluid system generated from the mixing of mantle-derived fluids with crustal-derived metamorphic fluids, and the ore-forming materials were upper crustal- or orogenic-derived. The alkali-rich intrusion-related Au mineralization is hosted in the Ordovician-Silurian sedimentary rocks and minor in the Paleogene alkaline intrusions, and the Au orebodies occur predominantly in the alteration halos. It contains a CO₂-bearing, largely metamorphic-sourced mesothermal fluid system, and the ore-forming materials were derived from the ore-hosting rocks and minor from the alkali-rich intrusions. The porphyry Cu-Mo-Au mineralization occurs in the granite/syenite porphyries and/or along their contact skarn, with the mineralizing fluids being magmatic-hydrothermal in origin. The former two hypogene Au mineralization types in Jinping were mainly formed in the late Eocene (ca. 34–33 Ma) and slightly after the porphyry Cu-Mo-Au mineralization (ca. 35–34 Ma), which is coeval with the regional Himalayan orogenic event. Subsequent weathering produced the laterite Au mineralization above or near the hypogene Au orebodies.  相似文献   

中国大陆克拉通地体地壳密度结构特征   总被引：1，自引：0，他引：1  

杨文采  瞿辰  侯遵泽  颜苹  于常青 《地质论评》2017,63(4):843-853

本文根据重力场小波变换的尺度—源深度转换律,进行地面重力异常场多尺度分解,取得了反映中国地壳不同埋藏深度的小波细节,揭示了克拉通地体地壳的密度结构。中国大陆克拉通地体地壳密度结构的总体特点是:地壳密度总体偏高,尤其是在经历了岩浆底垫作用后,下地壳形成了粗大的和高密度的壳根,而造山带的下地壳通常有低密度的山根。现今的克拉通地体有几个演化的阶段,由陆地核演化为一定规模的克拉通地体可能经历漫长的时间。不同演化的阶段地体的物理性质有明显的变化,要赋予大地构造单元以演化阶段的内涵,才能准确理解它们的行为和属性。同时,根据地壳密度结构成像的结果,可以了解克拉通地体的成熟度。中国大陆克拉通地体或者内部地块的地壳密度结构大致可以分为三类。上中下地壳密度都偏高的属于第一类,称为典型的克拉通,塔里木、阿拉善、华北东部、上中扬子等属于第一类。第二类克拉通地体上地壳密度偏低,而下地壳密度偏高,称为弱结晶基底的克拉通,鄂尔多斯和佳木斯属于第二类。第三类上中地壳密度偏高,而下地壳密度偏低,称为无壳根的克拉通残片,柴达木和准噶尔盆地属于此类,它们可能是古克拉通地体的残片。  相似文献   

Geochemistry, Geochronology and Lu-Hf Isotopes of Peraluminous Granitic Porphyry from the Walegen Au Deposit, West Qinling Terrane     

GUO Xianqing  YAN Zhen  Jonathan C. AITCHISON  FU Changlei  WANG Zongqi 《《地质学报》英文版》2017,91(6):2024-2040

Walegen Au deposit is closely correlated with granitic intrusions of Triassic age, which are composed of granite and quartz porphyries. Both granite porphyry and quartz porphyry consist of quartz, feldspar and muscovite as primary minerals. Weakly peraluminous granite porphyry(A/CNK=1.10–1.15) is enriched in LREE, depleted in HREE with Nb-Ta-Ti anomalies, and displays subduction-related geochemistry. Quartz porphyry is strongly peraluminous(A/CNK=1.64–2.81) with highly evolved components, characterized by lower TiO_2, REE contents, Mg~#, K/Rb, Nb/Ta, Zr/Hf ratios and higher Rb/Sr ratios than the granite porphyry. REE patterns of quartz porphyry exhibit lanthanide tetrad effect, resulting from mineral fractionation or participation of fluids with enriched F and Cl. LAICP-MS zircon U-Pb dating indicates quartz porphyry formed at 233±3 Ma. The ages of relict zircons from Triassic magmatic rocks match well with the detrital zircons from regional area. In addition, ε_(Hf)(t) values of Triassic magmatic zircons from the granite and quartz porphyries are -14.2 to -9.1(with an exception of +4.1) and -10.8 to -8.6 respectively, indicating a crustal-dominant source. Regionally, numerous Middle Triassic granitoids were previously reported to be formed under the consumption of Paleotethyan Ocean. These facts indicate that the granitic porphyries from Walegen Au deposit may have been formed in the processes of the closing of Paleotethyan Ocean, which could correlate with the arc-related magmatism in the Kunlun orogen to the west and the Qinling orogen to the east.  相似文献   

西藏拉萨地块南缘雄村矿集区首次发现早石炭世辉长岩:古特提斯洋的残留?   总被引：1，自引：0，他引：1  

郎兴海  唐菊兴  邓煜霖  谢富伟  杨宗耀  崔志伟  王旭辉  李志军  张忠  张金树  黄勇 《地球学报》2017,38(5):745-753

拉萨地块是研究特提斯洋形成演化和青藏高原陆内汇聚作用的关键地区,前人对拉萨地块中新生代构造演化过程进行了大量的研究,而对于古生代演化阶段研究较为薄弱。本文以拉萨地块南缘雄村矿集区新发现的辉长岩为研究对象,对雄村辉长岩进行锆石LA-ICP-MS U-Pb定年,探讨其反映的构造意义。雄村辉长岩中锆石LA-ICP-MS U-Pb年龄为(341.55±0.89)Ma,表明其形成于早石炭世。结合区域地质演化过程,认为早石炭世雄村辉长岩可能是古特提斯洋的残留,新的年龄数据将为研究拉萨地块和特提斯洋的演化过程提供重要的约束。  相似文献   

保山镇康地块矽卡岩型铅锌矿床成因初探   总被引：4，自引：0，他引：4  

杨玉龙  叶霖  程增涛  鲍谈  高伟 《岩石矿物学杂志》2012,31(4):554-564

保山镇康地块是"三江"南段重要的铅锌多金属成矿区之一,地质构造复杂,铅锌成矿地质条件优越,其中核桃坪与芦子园是近年发现的两个大型铅锌矿床,矿床受近NE向断裂、背斜轴部和地层控制明显,上寒武统核桃坪组与沙河床组大理岩化灰岩为主要赋矿地层,近矿围岩矽卡岩化强烈,流体包裹体,Pb、S、H、O同位素和微量元素等地球化学对比研究表明:核桃坪和芦子园铅锌矿床均经历了中温、高温两个矿化阶段;核桃坪铅锌矿床矿石铅同位素较芦子园铅锌矿床有较高的比值和较大的变化范围,均以高μ值为特征,属于放射性成因铅,暗示其成矿物质以壳源铅为主;硫化物硫同位素均多为较低正值并呈塔式分布,具有岩浆硫特征,两者均无生物硫酸盐热化学还原作用的参与,其中硫同位素分馏已达平衡;与硫化物共生的石英δDH2O(-109‰~-91‰)和δ18OH2O(-4.3‰~2.3‰)同位素研究表明核桃坪矿床成矿流体主要来自深部岩浆水,并遭受后期大气降水或地层水的混合;核桃坪矿床与芦子园矿床的微量元素具有岩浆热液型矿床特征,不同于VMS型、MVT型铅锌矿床。因此,笔者认为两个矿床应属于与深部隐伏岩体有关的中-高温矽卡岩型铅锌矿床,矿区深部隐伏岩体的侵入产生岩浆热液并携带Pb、Zn等成矿物质与地层水或大气降水混合,在背斜轴部与NE向断裂的交汇处形成该类型矿床。  相似文献   

Refertilization of serpentinites in the Sulu UHP terrane,Eastern China: constraints from geochronology,mineral composition,geochemistry, and Re–Os isotopes     

《International Geology Review》2012,54(15):1897-1913

ABSTRACT

Serpentinites from Junan (JN), Rizhao (RZ), and Rongcheng (RC) in the Sulu ultra-high-pressure (UHP) terrane, China, were analysed for U–Pb zircon geochronology, mineral chemistry, whole-rock major and trace element chemistry (including rare-earth elements (REEs) and platinum-group elements (PGEs)), and Re–Os isotopes, in order to better constrain their petrogenesis and geodynamic process. The serpentinite zircons yield two age groups: 731 ± 10 to 780 ± 10 Ma for relic magmatic zircon cores, which may indicate early crystallization and emplacement of the peridotite in the Yangtze crust, and 209 ± 2 to 218 ± 3 Ma for metamorphic zircon, which coincides with Triassic UHP metamorphism. The spinels in the serpentinites exhibit significant Cr# variation (0.6–0.91) and have undergone multi-stage metamorphism. The serpentinites are characterized by enrichment in incompatible trace elements, low Ni and IPGE concentrations, and high Pd/Ir ratios, and the bulk-rock major elements plot in the ultramafic cumulate region. Their Re and Os concentrations are similar to those of typical orogenic peridotite, but they have high ¹⁸⁷Os/¹⁸⁸Os ratios (0.12433–0.14423). We believe that the serpentinite’s protolith consisted of cumulates from an asthenosphere-derived melt that intruded into the continental crust of the Yangtze craton in the Neoproterozoic. These cumulates were later subducted and metamorphosed during the subduction of the Yangtze craton in the Triassic. The serpentinites underwent melt–rock interactions and fluid enrichment, both prior to and during serpentinization.  相似文献   

The tectono-magmatic evolution of the West Junggar terrane (NW China) unravelled by U–Pb ages of detrital zircons in modern river sands     

《International Geology Review》2012,54(5):607-621

ABSTRACT

The West Junggar terrane (WJT) is an outstanding laboratory for studying the tectonic evolution of the Junggar–Balkhash Ocean, because it contains widespread Paleozoic magmatism in different tectonic settings. We attempt to reconstruct the tectono-magmatic evolution of WJT through U–pb analysis of detrital zircons from three modern river sand samples from the Harabura, Baibuxie, and Aletengyemule rivers in the Barleik Mountains of the central WJT. A total of 232 concordant spots show Th/U ratios of 0.14–1.69, typical of igneous origin, and they contain abundant Paleozoic (96%) and few Precambrian (4%) ages, with major age populations at 450–530, 400–430, 320–380, and 265–320 Ma. The first two groups may be derived from the early subduction- and accretion-related magmatic rocks of the WJT, whereas the third group is congruent with magmatic activities related to the final subduction and basin-filling processes within a framework of the remnant Junggar–Balkhash Ocean. By combining with the regional data, the last group of magmatic events is referred to as post-subduction magmatism. The missing Mesozoic–Cenozoic magmatism clearly indicates a pre-Permian closure for the Junggar–Balkhash Ocean, nearly coeval with the closure of other oceans in the southwestern Palaeo-Asian Ocean.  相似文献   

Kinematics of the Guerrero terrane accretion in the Sierra de Guanajuato,central Mexico: new insights for the structural evolution of arc–continent collisional zones     

《International Geology Review》2012,54(5):574-589

The Guerrero terrane comprises Middle Jurassic–Early Cretaceous arc successions that were accreted to the North American craton in the late Early Cretaceous, producing closure of the Arperos oceanic basin and the formation of an approximately 100 km-wide fold–thrust belt. Such a suture is key to investigating the structural evolution related to Guerrero terrane accretion and, in general, to arc–continent collisional zones. The Sierra de Guanajuato is an exposure of the Guerrero terrane suture belt and consists of a complex tectonic pile that formed through at least three major shortening phases: D1SG, D2SG, and D3SG (SG, Sierra de Guanajuato). During the D1SG and D2SG phases, the Upper Jurassic–Lower Cretaceous successions of the Arperos Basin piled up, forming a doubly vergent imbricate fan of thrust sheets that accommodated substantial NE–SW shortening. Mylonite microtextures, as well as syntectonic minerals, indicate that the D1SG and D2SG deformation events took place under low greenschist-facies metamorphic conditions. We relate these deformation phases to the progressive NE migration of the Guerrero terrane, which triggered the collapse and closure of the Arperos Basin. During D3SG, the El Paxtle arc assemblage of the Guerrero terrane was tectonically emplaced onto the previously deformed successions of the Arperos Basin. However, D3SG structures indicate that during this deformational stage, the main shortening direction was oriented NW–SE and that contraction was accommodated mostly by SE-vergent ductile thrusts formed under low greenschist-facies metamorphic conditions. We suggest that the top-to-the-SE emplacement of the El Paxtle assemblage may be a result of the tectonic escape of the arc produced by the continuous NE impingement of the Guerrero terrane during its collisional addition to the Mexican mainland.  相似文献